I. Field of the Invention
The present invention relates to an image sensor, in particular a CMOS image sensor, for electronic cameras having a plurality of light-sensitive pixels which are arranged in rows and columns and whose signals are conducted via a plurality of column lines to column amplifiers, with a column amplifier being associated with each column line.
II. Description of Related Art
Known electronic cameras include an image sensor which comprises a plurality of light-sensitive elements or pixels which are arranged in rows and columns and which convert light incident through a lens of the camera into electrical signals. For the reading out of an image, each of the pixels is addressed, with each pixel corresponding to a respective picture element of the image, and a signal which is proportional to a charge of the pixel collected by an exposure is conducted to an output of the image sensor.
Such an image sensor has a separate row selection line for each row and at least one separate column line for each column.
The reading out of such an image sensor usually takes place linewise, i.e. line for line. For this purpose, the pixels of the respective row are switched to the column lines by means of the respective row selection line. A separate column amplifier is associated with each of the column lines to amplify the signals of the selected pixels applied to the column lines. The amplified signals are then conducted to the output via a multiplexer device or—if a plurality of outputs are provided, as is preferred to achieve a high picture rate—to the outputs of the image sensor. The named column amplifiers are therefore arranged between the light sensitive elements and the multiplexer device with respect to the signal readout direction.
To achieve a high dynamic range for the image sensor, the pixels and the column amplifiers are made with very low noise and thus particularly sensitive. Small signal aliasing thereby already results in an aliased brightness of the picture element corresponding to the respective amplified signal. Such a defect can, however, not be perceived by the eye provided that it occurs randomly.
If signal aliasing is, however, caused by a column amplifier, the defect occurs in all pixels of the column of the image sensor associated with the column amplifier and thus in all picture elements of the corresponding column of the image so that a vertical stripe becomes visible in the image which can be perceived by the eye. It is very probable due to the high number of column amplifiers that an individual column amplifier differs greatly from the other column amplifiers and causes such perceptible signal aliasing.